A cutting blade comprising a circular disc having teeth located around the periphery thereof or around an edge portion thereof is known from the U.S. Pat. No. 1,083,645. Slots are formed in that part of the disc which is located between the inner part of the disc and the toothed peripheral edge part thereof.
The purpose of this design is to reduce the tendency of the blade to warp as a result of expansion of the toothed portion of the disc (changes in length) caused by frictional heat generated by contact of the teeth with the material being cut, and as a result of centrifugal forces acting on the peripheral portions of a rotating disc.
When the toothed peripheral edge portion of a cutting disc warps as a result of changed in length, the cutting groove in the material being worked becomes wider, which greatly impairs the economy, especially when ripping trees.
In the U.S. Pat. No. 1,083,645 it is proposed that slots shall be so formed in the blade parts located between the inner part of the blade and its peripheral edge part that intermediate blade or material sections have a curved configuration and are oriented approximately radially at their inner portions and extend outwardly therefrom to terminate tangentially with respect to the direction of rotation of the blade. According to the descriptive part of this specification the added purpose of this design is to transfer the drive force from the centre of the blade to the toothed edge portion thereof, through the agency of a substantially tangentially acting tensile force.
It is known to use in sawmills circular saw blades provided with hardmetal teeth inserts, so as to reduce wear of the blades and therewith reduce the number of stoppages required for blade changes. The saw blade normally has a diameter of from 0.7 to 1.2 meters, and the hardmetal inserts have a width which varies between 4 and 5 mm, while the thickness of the disc is between 3 and 4 mm.
As beforementioned, when in use the blade, and then primarily the radially outer parts of the blade, becomes hot, causing said peripheral blade parts to expand. This localised expansion of the blade promotes the risk of warping at the peripheral parts of the disc. Warping results in a wider cutting groove with a reduction in yield as a consequence thereof, and also in troublesome vibrations which may be so bad as to cause damage to the saw and equipment.
Other means have been proposed with the intention of reducing the warping tendencies of the toothed peripheral edge of a cutting blade caused by the concentration of heat in the peripheral areas of the blade when at work, and also the frictional heat generated by a warped blade in contact with the surfaces of the cutting groove Thermal extension of the central parts of the blade disc can be mentioned as an example of such means. No simple effective solution to the problem has been proposed, however.